Processing device and image forming device

ABSTRACT

After post-processes have been performed on sheet bundles which have been stacked in a post-processing tray  16 , the sheet bundles are alternately shifted in the paper conveyance lateral direction and each of these shifted sheet bundles are conveyed from the post-processing tray  16  to the discharge port by a sheet receiving member  18 , and the sheet bundle is discharged in the shifted condition to a paper discharge tray  13  by a pair of discharge rollers  12  which are located at the discharge port. The pair of discharge rollers  12  have an upper discharge roller  22  and an opposing lower discharge roller  24  which open and close freely, and a solenoid for switching between a closed condition which grasps the sheet bundle and an opened condition which does not grasp the sheet bundle. The lower discharge roller  22  and the upper discharge roller  24  are closed by the solenoid  40  at predetermined timing based on the sheet size.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a post-processing device, andparticularly a processing device which performs post-processing such asstapling of bundles of sheets onto which an image has been formed. Theinvention further relates to an image forming device such as a copier,printer, fax machine, or a multifunction machine thereof equipped withthis post-processing device.

2. Background Information

Conventionally, post-processing devices are connected to or built intoimage forming devices such as multifunction machines or the like. Thesepost-processing devices stack multiple sheets (copy paper, OHP film, orthe like) which have completed printing on a post-processing tray, andthen staple bundles of these sheets or perform sorting or the like inthe post-processing tray.

With these post-processing devices, the sheet bundles must be smoothlydischarged to a sheet discharge tray or the like external to the devicein order to smoothly perform the alignment operation, which is a leadingoperation to the post-processes, and to prevent problems with bending,wrinkling, or tearing of the thick sheet bundles after thepost-processing, and various technologies have been proposed for thispurpose.

For instance, as shown in FIG. 7, the technology disclosed in JapaneseLaid Open Patent Application No. 2002-167115 (Patent Reference 1) has apair of discharge rollers 100 consisting of a bottom discharge roller101 and a top discharge roller 102 which has a closed position where therollers 101, 102 are in contact and form a nip, and an open positionwhere both rollers 101, 102 are separated to allow passage of a sheetbundle. With these conventional post-processing devices 103, bothrollers 101, 102 are mutually compressed by the forces of a spring 104when the pair of discharge rollers 100 is in the closed position.Furthermore, the bottom discharge roller 101 and the top dischargeroller 102 are separated against the force of the spring 104 when thepair of discharge rollers 100 is in the open position, and thereforebundles of large-size sheets (A3, B4, 11×17, 8.5×14 or the like) caneasily pass through the pair of discharge rollers 100.

When the pair of discharge rollers 100 is in the open position, a lever106 will rotate in the clockwise direction and the lead edge of thelever 106 will push down on the upstream side of an upper dischargeguide 108, when a solenoid 105 is turned ON. Thereby the upper dischargeguide 108 will rotate in the clockwise direction of the figure with afixed shaft 107 as a fulcrum, and the upper discharge roller 102 will bemoved above and away from the bottom discharge roller 101. Furthermore,when the upper discharge guide 108 rotates, the fulcrum shaft 109 willmove downward and the bottom discharge guide 110 will rotate in theclockwise direction of the figure with a fulcrum shaft 111 as thefulcrum. Thereby the lower discharge guide 110 will move to the upperposition until the top surface passes the outer circumference surface ofthe bottom discharge roller 101, and the sheet bundle is able tosmoothly pass through without contacting the outer circumferentialsurface of the bottom discharge roller 101.

Furthermore, the technology disclosed in Japanese Laid Open PatentApplication No. H11-92019 (Patent Reference 2) moves the pair ofdischarge rollers from the open state to the closed state (nip state)when the trailing end of the sheet bundle in the direction of conveyancereaches a position 80 mm before passing through the pair of dischargerollers, and closes the pair of discharge rollers after most of thesheet bundle has passed through the pair of discharge rollers (openstate) in order to minimize vertical staggering of the sheet bundle.

However, with the conventional technology of Patent Reference 1, when asmall size sheet bundle is discharged with the lower discharge roller101 and the upper discharge roller 102 of the pair of discharge rollers100 in the closed state (nip state), the sheet bundle will be verticallystaggered, the staggering force will act on the stapling region, andstapled sheet bundle will easily become damaged. Furthermore, there is apossibility that unstapled sheet bundles will become staggered oralignment defects will occur (If the curl is severe or if there are manysheets, the sheets near the lower discharge roller 101 side will beconveyed first). Furthermore, even when a large sheet bundle isdischarged, the staple bundle will have problems with bundle staggeringand alignment defects.

Furthermore, when only a fixed location (80 mm) from the trailing end ofthe sheet bundle in the conveyance direction is nipped as with theconventional technology of Patent Reference 2, and the sheet bundlestapling is a single point binding in the corner, if multiple sheetbundles are discharge to the discharge tray, the multiple sheet bundleswhich have been discharged will form an incline and drop out. In thiscase, the multiple sheet bundles which have been stapled may bealternately shifted in a direction orthogonal to the paper conveyancedirection, but when the sheet bundles are shifted in the directionorthogonal to the paper conveyance direction, the center of gravity inthe direction orthogonal to the sheet bundle will protrude from a pushup member which receives and conveys the trailing end of the sheetbundle, and conveyance problems will occur such as the sheet bundle willbe conveyed at an incline when being conveyed. Therefore, if a location80 mm from the trailing end of the sheet bundle in the conveyancedirection is nipped and the pair of discharge rollers close after mostof the sheet bundle has been pushed up, the sheet bundle will becomeinclined and drop out during conveyance prior to the sheet bundle beingnipped by the pair of discharge rollers.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a post-processingdevice and an image forming device which can shift each sheet bundle inorder to prevent conveyance problems with the sheet bundle afterpost-processing, and enable discharging to the discharge trade in ashifted state.

A first aspect of the present invention is a post-processing devicewhich stacks multiple sheets on a post-processing tray after performingpost-processing on the multiple sheet bundles, alternately shifts eachsheet bundle in a direction that is orthogonal to the paper conveyancedirection, conveys each of the shifted sheet bundles from thepost-processing tray to a discharge port using sheet conveying means,and discharges the sheet bundles in a shifted state on to a sheetdischarging tray using a pair of discharge rollers positioned at thedischarge port, wherein:

the pair of discharge rollers has an upper discharge roller and anopposing lower discharge roller which freely open and close;

and further comprising driving means for switching the upper dischargeroller and the lower discharge roller between a closed state whichallows the sheet bundle to be grasped and discharged, and an openedstate where the sheet bundle is not grasped; and

wherein the lower discharge roller and the upper discharge roller areclosed by a controlling means at predetermined timing based on the sheetsize or the number of sheets.

A second aspect of the present invention is the post-processing deviceaccording to the first aspect, wherein the predetermined timing is for afixed period of time after the lead edge of the sheet bundle in theconveyance direction reaches the pair of discharge rollers.

A third aspect of the present invention is the post-processing deviceaccording to the first aspect, wherein the predetermined timing is for afixed period of time from the moment conveyance of the sheet bundle bythe sheet conveying means begins.

A fourth aspect of the present invention is the post-processing deviceaccording to any one of the first to third aspects, wherein the trailingend side of the sheet bundle in the conveyance direction is nipped basedon the sheet size of the sheet bundle.

A fifth aspect of the present invention is the post-processing deviceaccording to any one of the first to fourth aspects, wherein thetrailing end side of the sheet bundle in the conveyance direction isnipped as the number of sheets in the sheet bundle increases.

According to a sixth aspect of the present invention, an image formingdevice comprises an image forming unit which forms an image on a sheet,and the post-processing device according to any one of the first tofifth aspects for performing post-processing of sheets on to which animage has been formed.

With the present invention, a lower discharge roller and an upperdischarge roller positioned at a discharge port are closed atpredetermined timing based on the sheet size or the number of sheets, sothe post-processed sheet bundles can be bound in a shifted state so thatconveyance problems will not occur, and the post-processed sheet bundlescan be discharged on to the paper discharge tray without the sheetbundles becoming staggered. Furthermore, even when performingpost-processing of small size sheet bundles, damage to the sheet bundlecan be prevented by nipping by the pair of discharge rollers.

These and other objects, features, aspects and advantages of the presentinvention will become apparent to those skilled in the art from thefollowing detailed description, which, taken in conjunction with theannexed drawings, discloses a preferred embodiment of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a schematic block diagram of the post-processing device andimage forming device of the present invention;

FIG. 2 is a front view diagram of the lower unit of the post-processingdevice;

FIG. 3 is a cross-sectional side view of the same;

FIG. 4 is a diagram showing the construction of the pair of dischargerollers of the post-processing device;

FIG. 5 is a perspective view of the discharge port side of the pair ofdischarge rollers (closed state) of the post-processing device;

FIG. 6 is a perspective view of the discharge port side of the pair ofdischarge rollers (opened state) of the post-processing device; and

FIG. 7 is a diagram showing the construction of a pair of dischargerollers for a conventional post-processing device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment for carrying out the present invention will be describedin detail based on the drawings.

Simplified Structure of a Post-Processing Device and Image FormingDevice Equipped Therewith

FIG. 1 shows the simplified structure of the post-processing device 1 ofan embodiment of the present invention and an image forming device 2equipped therewith.

As shown in FIG. 1, a sheet (copy paper, OHP film or the like) 4 fedfrom a paper feed tray 3 is printed with an image by an image formingunit 5, and then conveyed along the sheet conveyance path 8 of thepost-processing device 1 by a pair of discharge rollers 7 on the side ofthe image forming device body 6. Incidentally, the operation forpunching holes in the sheet 4 is performed by a punch unit 5 establishedon the sheet conveyance path 8, so hereinafter, in order to simplify thedescription, post-processing refers to those processes other than thehole punching operation, such as stapling or the like. Ifpost-processing will not be performed, the sheet 4 which has beenconveyed along the sheet conveyance path 8 of the post-processing device1 is guided through the discharge path 11 by branched tabs 10 to a pairof discharge rollers 12 and is then conveyed onto a sheet dischargingtray 13 by the pair of discharge rollers 12. Furthermore, whenpost-processing will be performed, the sheet 4 which has been conveyedalong the sheet conveyance path 8 of the post-processing device 1 isconveyed through the post-conveyance path 14 by the branched tabs 10 tothe post-processing unit 15. The post-processing unit 15 comprises anupper unit 28 and a lower unit 29, a post-processing tray 16, and abending unit 19 or the like for bending stapled sheet bundles in themiddle.

FIG. 2 and FIG. 3 are front view and side view diagrams of the lowerunit 29. The sheet 4, which has been conveyed to the post-processingunit 15, is conveyed downward and the trailing end (trailing end in thedirection of conveyance to the paper discharge tray from thepost-processing unit 15) is received by a sheet receiving member (sheetconveying means) 18. The sheet receiving member 18 is mounted on a belt52 which rotates on two rotating shafts 50, 51. The sheet receivingmember 18 waits at a predetermined location in the direction of beltmovement based on the size of the sheet being used. Furthermore, theupper end of the lower unit 29 has a rotating shaft 58, and another belt60 revolves around this rotating shaft 58 and rotating shaft 50. Thisbelt 60 has a protrusion 59 which presses on the lead edge of the sheet(lead edge in the direction of conveyance to the paper discharge tray13) in order to align the sheets (Refer to FIG. 3).

The lower unit 29 has a pair of upper guides 53 and a pair of lowerguides 54 arranged in line in the paper conveyance lateral direction(hereinafter defined as the direction orthogonal to the sheet dischargedirection) in order to guide the sheet in the direction of conveyance.Both the pair of upper guides 53 and the pair of lower guides 54 areable to move symmetrically with regards to a centerline A in the paperconveyance lateral direction. A pair of double end support members 55are established in line in the paper conveyance lateral directionbetween the upper guides 53 and the lower guides 54. The double endsupport members 55 receive the trailing end of the sheet bundle ifstapling is to be performed, and have a near L-shaped receiving plate56. The double end support members 55 are moved in conjunction with thecorresponding lower guide 54 by an operating lever 57. If the length ofthe sheet in the conveyance direction is smaller than a predeterminedsheet size, the pair of lower guides 54 will spread outward, the lowerguides 54 will press on the operating lever 57, the double end supportmembers 55 will be pushed down by the operating lever 57 and move to abase position which supports the trailing end of the sheet as shown bythe line in FIG. 3. If the length of the sheet in the conveyancedirection is longer than the predetermined sheet size, the pair of lowerguides 54 will become narrow, the operating lever 57 will rotate freely,the double end support members 55 will push up on the operating lever57, and will move to the retreated position shown by the broken line inFIG. 3.

In this manner, if the length of the sheet in the direction ofconveyance is smaller than the predetermined sheet size, the multiplesheets 4 stacked in the post-processing tray 16 after being received bythe sheet receiving member 18 are post-processed such as stapling or thelike by the post-processing means 17 after moving the belt 60 downwardsand lightly pushing the lead edge of the sheet to the sheet receivingmember 18 side using a protrusion. This post-processing means 17 has 2center binding staplers 17 a and an angled binding stapler 17″established on the right side of FIG. 2. If the length of the sheet inthe conveyance direction is smaller than the predetermined sheet size,the double end support members 55 will be waiting at the base position,so the trailing end of the sheet bundle will be more stably supported bythe sheet receiving member 18 and the double end support members 55.

If the length of the sheet in the conveyance direction is longer than apredetermined sheet size, the sheet receiving member 18 will move to thebase position, and then the pair of lower guides will tighten, thedouble end support members 55 will rotate to the narrow position for thesheet receiving member 18 to move downward, and the trailing end of thesheet bundle will be supported only by the sheet receiving member 18.Furthermore, the plurality of sheets 4 which have been moved downward bythe sheet receiving member 18 are lightly pressed on the lead edge ofthe sheet to the sheet receiving member 18 side by the protrusion 59 toarrange and align the lead edge of the sheets, and then the belts 52, 60will simultaneously move upward, and the sheet receiving member 18 willreturn again to the base position before stapling will be performed.

At this time, in order to prevent the plurality of sheet bundles whichhave been discharged to the paper discharge tray 13 from stacking up toform an incline and falling off of the paper discharge tray 13, thestapled sheet bundles are alternately shifted in the paper conveyancelateral direction when discharged Therefore, the pair of upper guides 53will alternately move to both ends of the shift positions (not shown inthe drawings) so that the stapled sheet bundles will be dischargedupward by the sheet receiving member 18 in that position.

Structure of Pair of Discharge Rollers

FIG. 4 through FIG. 6 are diagrams which show the structure of the pairof discharge rollers 12 which are an embodiment of the presentinvention, and are block diagrams of the region shown by K in FIG. 1.

The pair of discharge rollers 12 are comprising a discharge upper guide21 which is rotatably supported to the device body 20 side at thelongitudinal center region, a plurality of upper discharge rollers 22which are rotatably supported on one end 21 a of the upper dischargeguide 21, a lower discharge guide 23 which is rotatably supported to thedevice body 20 side at the longitudinal center region, and a pluralityof lower discharge rollers 24 which are rotatably supported by thedevice body 20 side. These plurality of upper discharge rollers 22 andlower discharge rollers 24 are positioned at appropriate intervals inthe paper conveyance lateral direction (direction orthogonal to thesheet discharge direction), and therefore any size of sheet which issubject to post-processing by the post-processing device can positivelybe conveyed.

The lower discharge guide 23 is rotatably supported to the frame 26 ofthe device body 20 in the longitudinal center region by a support pin25. A lower discharge guide 23 is constructed such that acounterclockwise rotational moment on the fulcrum point (support pin 25)is generated by gravity. Furthermore, the lower discharge guide 23 issupported by a hooking member 27 formed in the frame 26 on the side ofthe device body 20 such that one end 23 a of the lower discharge guide23 on the lower discharge roller 24 side is further retracted than theouter surface of the lower discharge roller 24, when positioned in theclosed state where a nip P is formed between the lower discharge roller24 and the upper discharge roller 22.

Furthermore, a near U-shaped groove 30 with an opening towards the leadedge is formed on the other end 23 b of the lower discharge guide 23.This U-shaped groove 30 is made to lock with play to a connecting pin 31formed in the other end 21 b of the upper discharge guide 21 which willbe described later. The play between the connecting pin 31 and theU-shaped groove 30 is formed to create a maximum separation dimensionbetween the lower discharge roller 24 and the upper discharge roller 22.Incidentally, the lower discharge guide 23 is formed to guide movementof the sheet by the sheet guide plate 23 c.

The upper discharge guide 21 is rotatably supported in the longitudinalcenter region by a support pin 25 which is used in common with the lowerdischarge guide 23. The longitudinal center region of the upperdischarge guide 21 has a bias force applied by a spring 37 in adirection such that the upper discharge roller 22 is pushed to the lowerdischarge roller 24 side, and on the other end 21 b, a bias force isapplied by a solenoid 40 (driving means) in the direction whichseparates the upper discharge roller 22 from the lower discharge roller24. Furthermore, the solenoid 40 is turned on and off by a controllingmeans not shown in the drawings. The upper discharge guide 21 isattached such that the connecting pin 31 on the other end 21 b whichlocks with play into the U-shaped groove 30 of the lower discharge guide23 protrudes from the side surface.

The frame 26 on the side of the device body 20 is comprising a solenoid40, a lever 42 which is rotatably supported to the frame 26 by a supportpin 41, and a wire or the like connecting ring 44 which connects one end42 a of the lever 42 to an operating rod 43 of the solenoid 40.Furthermore, when the solenoid 40 is turned on, the lever 42 is pulledby the operating rod 43 of the solenoid 40, the lever 42 rotates in aclockwise direction, the other end (lead edge) 42 b of the lever 42pushes the other end 21 b of the upper discharge guide 21, and causesthe upper discharge guide 21 to rotate (in the clockwise direction)around the support pin 25.

If sheets which are not to have post-processing are discharged onto thepaper discharge tray 13 by the pair of discharge rollers 12, the upperdischarge guide 21 will be pushed by the spring force of the spring 37and the upper discharge roller 22 will apply pressure to the lowerdischarge roller 24 through the upper discharge guide 21. Thereby theconnecting region between the upper discharge roller 22 and the lowerdischarge roller 24 will be in the closed state wherein a nip P isformed, and the sheet will be conveyed by the pair of discharge rollers12 onto the paper discharge tray 13.

Furthermore, if a sheet bundle which has had post-processing isdischarged onto the paper discharge tray 13 by the pair of dischargerollers 12, the solenoid 40 will be turned on, and the solenoid 40 willrotate the lever 42 in the clockwise direction, and the lead edge 42 bof the lever 42 will apply pressure on the top surface of the other end21 b of the upper discharge guide 21, and the upper discharge guide 21will be made to rotate in the clockwise direction with the support pin25 as a fulcrum point. Thereby the upper discharge roller 22, which isrotatably supported on one end 21 a of the upper discharge guide 21,will separate from the lower discharge roller 24. When the upperdischarge guide 21 rotates in a clockwise direction with the support pin25 as a fulcrum point, the connecting pin 31, which is connected to theother end 21 b of the upper discharge guide 21, will contact the bottomedge of the U-shaped groove 30 of the lower discharge guide 23. Theposition where the connecting pin 31 contacts the bottom edge of theU-shaped groove 30 on the lower discharge guide 23 is the maximumseparation position for the upper discharge roller 22 and the lowerdischarge roller 24. Incidentally, the maximum dimension for theseparation between the upper discharge roller 22 and the lower dischargeroller 24 is set to be the approximate dimension where a bundle of 50sheets of approximately A4 size copy paper with an average paperweightof 80 g/m2 can pass through.

When one end 23 a of the lower discharge guide 23 separates from thelocking member 27 on the side of the device body 20, rotates togetherwith the upper discharge guide 21 in the clockwise direction with thesupport pin 25 as the center of rotation, and the one end 23 a rotatesto a position which protrudes past the outer surface of the lowerdischarge roller 24, the solenoid 40 will continue to function and theposition will be maintained. In this manner, the bottom sheet (backsurface side) of the sheet bundle discharged from the post-processingunit 15 by the sheet receiving member 18 will not come in contact withthe outer surface of the lower discharge roller 24, and the lead edgeside of the sheet bundle will smoothly pass through the gap between thelower discharge roller 24 and the upper discharge roller 22 withoutcatching, because one end 23 a of the lower discharge guide 23 protrudespast the outer surface of the lower discharge roller 24. Incidentally,the pair of discharge rollers 12 are made to be in the separated stateeven if the sheet size of the sheet bundle for post-processing is largeso that the lead edge of the sheet in the direction of conveyanceexceeds the nip P between the lower discharge roller 24 and the upperdischarge roller 22 and must protrude externally when the sheet bundleis discharged during the aligning operation for the sheets in thepost-processing unit 15. Thereby the aligning operation can smoothly beperformed for large sized sheet bundles.

Sheet Bundle Discharge Operation by the Post-processing Device

With this embodiment, when the sheet bundle is discharged from thepost-processing unit 15 by the sheet receiving member 18, the power tothe solenoid 40 will be turned off after a predetermined period of timewhen passage of the lead edge of the sheet bundle in the direction ofconveyance is detected by a detecting sensor 47, or the power to thesolenoid will be turned off after a predetermined period of time whenthe sheet bundle lifting operation (conveyance operation) by the sheetreceiving member 18 begins. By turning off the power to the solenoid 40,the sheet bundle which has been conveyed to the discharge port will begrasped by the closing of the lower discharge roller 24 and the openingdischarge roller 22, and will be conveyed onto the paper discharge tray13.

For instance, in FIG. 2 and FIG. 3, if the sheet receiving member 18 ismoved such that the sheet bundle is moved to the base position forperforming the post-processing and the sheet bundle is to be stapled,stapling will be performed after moving the sheet bundle to the stapleposition in the paper conveyance lateral direction. For instance, ifstaples are to be in symmetric locations with regards to the center ofthe sheet, the pair of upper guides 53 will be moved in the paperconveyance lateral direction, and stapling will be performed by a centerbinding stapler 17′. Furthermore, if stapling is to be done in onecorner of the sheet bundle, the pair of upper guides 53 will be moved tothe right edge (FIG. 2) in the paper conveyance lateral direction andstapling will be performed by an angle binding stapler 17″. Next, thefirst stapled sheet bundle will be moved to a first shift position(bundle lifting position), and the sheet bundle will be lifted anddischarged by the sheet receiving member 18. The sheet receiving member18 is attached to the belt 52, and therefore the sheet bundle will belifted out by the sheet receiving member 18 to the location of therotating shaft 50 shown in FIG. 3, and thereafter will be transferred tothe protrusion 59 and discharged to the pair of discharge rollers 12 bythe protrusion 59. The protrusion 59 moves the back side of the tray inconjunction with the counterclockwise rotation of the belt 60 when theconveyance upper end is reached, and is then returned to the originalposition. Furthermore, the second stapled sheet bundle is moved to theother shift position (bundle lifting position) in the paper conveyancelateral direction, and the sheet bundle is lifted up and discharged bythe sheet receiving member 18. Therefore, if there are a plurality ofsheet bundles, the shift position will be alternately changed whendischarging. Incidentally, if the sheet bundles are not to be stapled,the shift position is similarly alternately changed for each sheetbundle, and the sheet bundles are lifted up and discharged by the sheetreceiving member 18.

Incidentally, when considering bundle staggering and alignment problems,the timing for cutting (nip) the power to the solenoid 40 will should besuch that the trailing end of the sheet in the direction of conveyanceis as close as possible to the stapling position. However, when thesheet bundle is raised by the sheet receiving member 18, as shown inFIG. 2, problems will not occur from the start of lifting the sheetbundle until passing through the top end of the upper guide 53, butafter passing the upper guide 53, a guide will not be present on bothsides in the lateral direction and therefore, if the center of gravityin the lateral direction of the sheet bundle protrudes past the sheetreceiving member 18, the sheet bundle will be inclined and unstableduring conveyance, and there is a possibility that conveyance defectssuch as catching or the like could occur. To illustrate, if a sheetbundle is discharged while shifted in the lateral direction of thesheet, the center of gravity in the lateral direction of the sheet willprotrude past the sheet receiving member 18, and there is a possibilitythat the sheet bundle will become inclined during conveyance and thatconveyance defects will occur. Therefore, with this embodiment, nippingwill be performed in the appropriate position of the sheet bundle inorder to prevent bundle staggering and alignment defects during nipping.

For instance, if the stapled sheet bundle is A4 vertical or smaller, thesheet detection sensor 47 will detect the lead edge of the sheet bundle,and when one third of the sheet size in the direction of conveyance haspassed after the lead edge, the power to the solenoid 40 will be cutoff, and nipping will be performed. For instance, for the case of A4lateral, nipping will occur at approximately 70 mm which is one third ofthe total length from the lead edge of the sheet in the direction ofconveyance, and for the case of A4 vertical, nipping will occur atapproximately 100 mm which is ⅓ of the total length from the lead edgeof the sheet in the direction of conveyance. In this manner, nippingwill be performed at a position one third of the total length from thelead edge of the sheet in the direction of conveyance, so the sheetbundle will not become inclined or the like even after passing throughthe upper guide 53. Furthermore, the nipping will be performed at apoint one third of the total distance from the lead edge of the sheet inthe direction of conveyance, so damage caused by nipping smaller sheetbundles after stapling can be prevented.

Furthermore, if the stapled sheet bundle is larger than A4 vertical(such as B4 or A3 or the like), in order to prevent damage or the liketo the sheet bundle, first the sheet bundle is shifted by the lowerdischarge roller 24 without contacting the outer surface of the lowerdischarge roller 24 while the lower discharge roller 24 and the upperdischarge roller 22 are in the opened state, and then the bundle will belifted by the sheet receiving member 18. Furthermore, the timing whenthe power to the solenoid 40 is turned off and the lower dischargeroller 24 and the upper discharge roller 22 are closed, is set to be themoment where ⅖ of the sheet bundle has passed since the lead edge in theconveyance direction after the bundle has started being raised by thesheet receiving member 18. For instance, for the case of B4 vertical,nipping will occur at approximately 145 mm which is ⅖ of the totallength from the lead edge of the sheet in the conveyance direction, andfor the case of A3 vertical, nipping will occur at approximately 167 mmwhich is ⅖ of the total length from the lead edge of the sheet in theconveyance direction. In this manner, nipping will occur at a position ⅖of the total length from the lead edge of the sheet in the direction ofconveyance, so similar to when the size is smaller than A4 vertical, thesheet bundle will not become inclined or the like after passing theupper guide 53. Therefore, for sizes which are smaller than A4 verticalas well as for sizes which are larger than A4 vertical such as B4, or A3or the like, the sheet position where the lower discharge roller 24 andthe upper discharge roller 22 close will moved toward the trailing endas the sheet size increases (timing will be delayed).

Furthermore, with the present embodiment, the timing for turning off thepower to the solenoid 40 is delayed as the number of sheets in the sheetbundle increases, so nipping will be performed to the trailing end side.For instance, if the lower discharge roller 24 and the upper dischargeroller 22 close (nip) when half of the sheet size in the conveyancedirection passes after the lead edge in the conveyance direction whenthe number of sheets in the sheet bundle is 50 or higher, bundlestaggering will increase because the nipping force will be weaker as thenumber of sheets in the sheet bundle increases, even though the timingfor nipping is the same. Therefore, the timing for nipping is changedfor every 10 sheets in the sheet bundle, and as the number of sheets inthe sheet bundle increases, the timing for closing the lower dischargeroller 24 and the upper discharge roller 22 will be delayed. Forinstance, for 10 or fewer sheet bundles, nipping will occur 50 ms afterthe sheet detection sensor 47 is turned on.

For 20 or fewer sheets, nipping will occur 100 ms after the sheetdetection sensor 47 is turned on.

For 30 or fewer sheets, nipping will occur 150 ms after the sheetdetection sensor is 47 turned on.

For 40 or fewer sheets, nipping will occur 200 ms after the sheetdetection sensor 47 is turned on.

For 50 or fewer sheets, nipping will occur 250 ms after the sheetdetection sensor 47 is turned on.

Furthermore, in order to perform nipping at the same sheet position fromthe lead edge in the sheet conveyance direction, the timing for turningoff the power to the solenoid 40 should be faster as the discharge speedof the sheet bundles increases. For instance, if nipping at a position60 mm from the detection of the lead edge of the sheet (position ⅓ fromthe lead edge of the sheet in the conveyance direction), nipping isperformed 150 ms from the moment the sheet detection sensor 47 is ON ifthe discharge speed is 400 mm/sec.

If the discharge speed is 500 mm/sec, nipping is performed 120 ms afterthe sheet detection sensor is ON.

If the discharge speed is 600 mm/sec, nipping is performed 100 ms afterthe sheet detection sensor is ON.

However, as the discharge speed increases, a staggering force which iscreated in the vertical direction of the sheet bundle will act on thestaple region and damage will easily occur, so with this embodiment, thenipping location should be on the trailing end of the sheet. Forinstance, for the case of an A4 vertical sheet bundle, nipping isperformed at a position 100 mm from the lead edge of the sheet when thedischarge speed is 400 mm/sec.

Nipping is performed at a position 150 mm from the lead edge of thesheet when the discharge speed is 500 mm/sec.

Nipping is performed at a position 200 mm from the lead edge of thesheet when the discharge speed is 600 mm/sec.

The post-processing device and image processing device of the presentinvention can be used in combination with an image reading device suchas a scanner, or can be used for performing post-processing on a sheetbundle after reading an image.

Any terms of degree used herein, such as “substantially”, “about” and“approximately”, mean a reasonable amount of deviation of the modifiedterm such that the end result is not significantly changed. These termsshould be construed as including a deviation of at least ±5% of themodified term if this deviation would not negate the meaning of the wordit modifies.

This application claims priority to Japanese Patent Application No.2004-364148. The entire disclosure of Japanese Patent Application No.2004-364148 is hereby incorporated herein by reference.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. Furthermore, the foregoing description of theembodiments according to the present invention are provided forillustration only, and not for the purpose of limiting the invention asdefined by the appended claims and their equivalents.

1. A post-processing device, comprising: a post-processing tray forstacking sheets; post-processing means for performing post-processing onsheet bundles comprising a plurality of sheets which have been stackedin the post-processing tray; sheet conveying means for alternatelyshifting each sheet bundle post-processed by the post-processing meansin a direction orthogonal to a conveyance direction, and conveying eachof the shifted sheet bundles to a discharge port; a pair of dischargerollers for discharging sheet bundles which have been conveyed by thesheet conveying means from the discharge port, having an upper dischargeroller and an opposing lower discharge roller which freely open andclose in order to achieve a closed state where the sheet bundle can begrasped and discharged and an open state where the rollers are mutuallyseparated; a sheet discharging tray for receiving sheet bundlesdischarged by means of the pair of discharge rollers; driving means forswitching the upper discharge roller and the opposing lower dischargeroller between the closed state and the open state; and controllingmeans for controlling the timing for switching the lower dischargeroller and the upper discharge roller between the open state and theclosed state in response to the paper size or the number of sheets. 2.The post-processing device according to claim 1, wherein the controllingmeans switches from the open state to the closed state after a fixedperiod of time from the moment the lead edge of the sheet bundle in theconveyance direction reaches the pair of discharge rollers.
 3. Thepost-processing device according to claim 1, wherein the controllingmeans switches from the open state to the closed state after a fixedperiod of time from the moment sheet bundle conveyance by the sheetconveying means begins.
 4. The post-processing device according to claim1, wherein the controlling means controls the timing for switchingbetween the open state and the closed state in order to nip the trailingend side of the sheet bundle in the conveyance direction as the size ofthe sheet bundle increases.
 5. The post-processing device according toclaim 1, wherein the controlling means controls the timing for switchingbetween the open state and the closed state in order to nip the trailingend side of the sheet bundle in the conveyance direction as the numberof pages in the sheet bundle increases.
 6. An image forming device,comprising: an image forming unit for forming an image on a sheet; apost-processing device for performing post-processing on a sheet ontowhich an image is formed by the image forming unit; the post-processingdevice comprising: a post-processing tray for stacking sheets;post-processing means for performing post-processing on sheet bundlescomprising a plurality of sheets which have been stacked in thepost-processing tray; sheet conveying means for alternately shiftingeach sheet bundle post-processed by the post-processing means in adirection orthogonal to a conveyance direction, and conveying each ofthe shifted sheet bundles to a discharge port; a pair of dischargerollers for discharging sheet bundles which have been conveyed by thesheet conveying means from the discharge port, having an upper dischargeroller and an opposing lower discharge roller which freely open andclose in order to achieve a closed state where the sheet bundle graspedand discharged and an open state where the rollers are mutuallyseparated; the sheet discharging tray for receiving sheet bundlesdischarged by means of the pair of discharge rollers; driving means forswitching the upper discharge roller and the opposing lower dischargeroller between the closed state and the opened state; and controllingmeans for controlling the timing for switching the lower dischargeroller and the upper discharge roller between the opened state and aclosed state in response to the paper size or the number of sheets. 7.The image forming device according to claim 6, wherein the controllingmeans switches from the open state to the closed state after a fixedperiod of time from the moment the lead edge of the sheet bundle in theconveyance direction reaches the pair of discharge rollers.
 8. The imageforming device according to claim 6, wherein the controlling meansswitches from the opened state to the closed state after a fixed periodof time from the moment sheet bundle conveyance by the sheet conveyingmeans begins.
 9. The image forming device according to claim 6, whereinthe controlling means controls the timing for switching between theopened state and the closed state in order to nip the trailing end sideof the sheet bundle in the conveyance direction in response to the sizeof the sheet bundle.
 10. The image forming device according to claim 6,wherein the controlling means controls the timing for switching betweenthe opened state and the closed condition in order to nip the trailingend side of the sheet bundle in the conveyance direction as the numberof pages in the sheet bundle increases.